This invention relates to an advance mechanism for a mine roof support unit.
A known type of mine roof support assembly is constituted by a plurality of roof support units positioned side-by-side along, for example, a longwall face. Each of the units has a roof shield supported on a floor sill by means of hydraulic props. The floor sill is constituted by a pair of spaced-apart floor girders. In order to advance the assembly to follow the advance of the longwall face, the roof support units are advanced, individually or in groups, by means of hydraulic advance rams. During the advance of any given unit, its hydraulic props are relaxed so that its roof shield is not under load.
A known type of advance mechanism for such a roof support unit comprises a pair of resilient relay rods and a hydraulic advance ram. Such an advance mechanism is positioned between the two floor girders of the roof support unit. The front (face-side) ends of the relay rods are attached, for example, to a longwall conveyor, and the rear (goaf-side) ends are coupled together by means of a guide element. The advance ram acts on the guide element, the floor girders providing an abutment for the ram. The guide element is longitudinally displaceable in grooves provided in the mutually-facing sides of two guide rails attached to the mutually-facing sides of the floor girders. (A typical prior art arrangement is disclosed in DE-OS No. 2540091).
The disadvantage of this known type of advance mechanism is that the advance mechanism tends to jam inbetween the floor girders. This jamming arises because the gap between the floor girders is relatively narrow, and because the advance ram is supported at the sides of the floor girders. Thus, as the advance ram is extended, the floor girders are subjected to a torque which tends to move their goaf-side ends towards one another. If such movement does occur to any appreciable extent, the advance mechanism will jam against the sides of the floor girders.
The aim of the invention is to provide an advance mechanism for a mine roof support unit which does not jam against the floor girders of the unit during use.